FIG. 1 illustrates one example of a prior known gas turbine engine in which a strut of the invention might be used. With reference to FIG. 1, a gas turbine engine is generally indicated at 10, having a principal and rotational axis 11. The engine 10 comprises, in axial flow series, an air intake 12, a propulsive fan 13, a high-pressure compressor 14, combustion equipment 15, a high-pressure turbine 16, a low-pressure turbine 17 and an exhaust nozzle 18. A nacelle 20 generally surrounds the engine 10 and defines the intake 12.
The gas turbine engine 10 works in the conventional manner so that air entering the intake 12 is accelerated by the fan 13 to produce two air flows: a first air flow into the high-pressure compressor 14 and a second air flow which passes through a bypass duct 21 to provide propulsive thrust. The high-pressure compressor 14 compresses the air flow directed into it before delivering that air to the combustion equipment 15.
In the combustion equipment 15 the air flow is mixed with fuel and the mixture combusted. The resultant hot combustion products then expand through, and thereby drive the high and low-pressure turbines 16, 17 before being exhausted through the nozzle 18 to provide additional propulsive thrust. The high 16 and low 17 pressure turbines drive respectively the high pressure compressor 14 and the fan 13, each by suitable interconnecting shaft.
Other gas turbine engines to which the present disclosure may be applied may have alternative configurations. By way of example such engines may have an alternative number of interconnecting shafts (e.g. three) and/or an alternative number of compressors and/or turbines. Further the engine may comprise a gearbox provided in the drive train from a turbine to a compressor and/or fan.
It is necessary within a gas turbine engine such as that of FIG. 1 to provide structural support for the engine rotors (be they in the fan, compressor or turbine section of the engine). This has been achieved in prior known designs by means of ball and roller bearings. The bearings are directly or indirectly attached to static bearing support structures, which provide a load path across the annulus by means of discrete struts. At the relatively cold end of the engine (e.g in the fans and compressor) these struts can be exposed to the annulus gas stream and even double as aerodynamic vanes. However, in hot turbine environments, the very high temperature annulus air can prohibit structural vanes. In such cases it is often necessary to isolate the struts from the hot annulus air by passing them through hollow, cooled, turbine vanes. FIG. 2 illustrates such a prior known arrangement.
In the turbine arrangement of FIG. 2, alternate rotating 22 and static 23 rows of a turbine are shown. The static row 23 comprises an array of hollow vanes 24. The rotating rows comprise a disc 25 rotatably mounted in a bearing 26. An outer perimeter of the disc 25 provides an array of retaining slots 27 into which blades (not shown) can be received. The hollow vanes 24 span an annular space which is bounded by a radially inner end wall 28 and a radially outer end wall 29. As can be seen a strut 30 is provided to extend through the hollow vane 24. The strut 30 passes from beneath a hub wall 28a of the support structure, through the radially inner end wall 28 and vane 23 and is secured in position by a spigot 31 extending from outside of the radially outer end wall 29, through the casing 29a and into a recess 32 provided in the strut 23.
FIG. 3 shows the strut fastening arrangement of FIG. 2 to the casing 29a in more detail. As can be seen the spigot is in the form of hollow dowel 31 which passes through a casing wall 29a and into recess 32 of the strut 30. A radial bolt is driven through dowel 31 and the recess 32 and screwed into position by means of complementary screw threads 34 provided in the strut 30 recess 32 and on the shaft of bolt 33.
In an assembled turbine, the struts 30 are typically interspersed around the circumference of the hub wall 28a between service tubes (not shown) resulting in a spoked structure. The spoked structure has the non-structural vanes 24 installed over the struts 30 and service tubes before being fitted into the outer casing 29a. Once in the outer casing 29a, the previously described spigot (hollow dowel 31) and radial bolt 33 arrangement is used to secure the struts 30 with respect to the casing 29a. 
The tolerance control required for the outside diameter to the struts and the positioning of the radial holes for the hollow dowels 31 previously required top level machining of the spoked assembly. (i.e. with the struts already attached). As the tolerance control could not be maintained if the struts were removed and then re-installed, it was considered desirable to specify a permanent attachment method for the struts 30 in the region of the hub wall 28a. Bolted joints were considered undesirable. Welding has been considered as an alternative, but the weld bead at heat affected zone of the weld has been found greatly to reduce the material properties in the region of the weld and significantly increase the likelihood of defects. Consequently spigot location has been adopted as a method of permanently attaching the struts 30 onto a bearing support structure. The arrangement uses abutment shoulders arranged externally of the annulus extending to form an abutment arms 37 through which cross pins are received to secure the struts 30 to a bearing support structure which is enclosed by the hub wall 28a. 
FIG. 4 shows the strut fastening arrangement of FIG. 2 at the hub wall 28a in more detail. As can be seen the strut 30 passes from the annulus and through the radially inner end wall 28 where a region adjacent an end of the strut 30 flares before extending as an abutment arm 37 with a uniform cross-section. An abutment shoulder 34 is defined by a recess in the arm 37 adjacent the flared region in a direction distal to the radially inner end wall 28. An integrally formed spigot defines a through hole in the hub wall 28a into which the strut 30 is received. The spigot may be formed integrally with the hub wall 28a or optionally comprises a separate component. A hole passes through the abutment arm 37 and receives a cross pin 36. A fillet radius 35 of the spigot defines an abutment rim which abuts the abutment shoulder 34 serving to restrict movement of the strut 30 along a radius of the annulus.